1. Field of the Invention
The present invention relates to a vibration-sensing element for supporting a first tine and a second tine to allow propagation of vibrations between the first and the second tines, where the first tine vibrates along an X axis of rectangular coordinate axis.
2. Description of the Related Art
Vibration-sensing elements having a pair of tines detect the angular velocity by making the tines vibrate along a predetermined axis.
In the following description, it is assumed that a tine vibrates along an X axis in the plane which contains rectangular coordinate axis (X-Y plane). When the tine vibrating along the X axis rotates around a Z axis perpendicular to the X-Y plane, the angular velocity generates the Coriolis force which acts on the tine along a Y axis. The Coriolis force depends upon the angular velocity. The angular velocity acting on the tine can be determined by measuring the Coriolis force indirectly as a displacement of the tine or directly using the piezoelectric effects of piezoelectric elements. A vibration-sensing gyro having a pair of tines as a tuning fork is disclosed in INTERNATIONAL LAYING-OPEN GAZETTE W090/10196 whereas an H-shaped vibration-sensing element is specified in JAPANESE UTILITY MODEL LAYING-OPEN GAZETTE No. H-1-81514.
Such a vibration-sensing gyro is mounted on a vehicle to detect the yaw rate generated in turning the vehicle or to record the running conditions of the vehicle.
The vibration-sensing element proposed in INTERNATIONAL LAYING-OPEN GAZETTE W090/10196 is composed of a quartz crystal, and excites vibrations (excited vibrations) of each tine by means of electrodes and detects vibrations (detected vibrations) of the tine with the electrodes. In this structure, a method of regulating the mass is proposed to make the resonance frequency of the excited vibrations of each tine coincide with the resonance frequency of the detected vibrations. A technique of such mass regulation is disclosed in JAPANESE UTILITY MODEL LAYING-OPEN GAZETTE No. H-1-81514. In this structure, each tine has an additional weight integrally formed therewith via a constricted portion. The additional weight is melted and removed according to the measurement of the resonance frequencies of the respective tines.
The mass regulation method described above requires measurement of the resonance frequencies simultaneously with fusion and removal of a specific weight while not allowing measurement of the specific weight melted and moved from the tine. In the conventional method, it is further required, based on the reasons described below, to make the resonance frequencies in the direction of the excited vibrations of the respective tines coincide with each other as well as to make those in the direction of the Coriolis force-induced vibrations or the detected vibrations coincide with each other. The adjustment of the resonance frequencies according to the conventional method accordingly requires a great deal of skill.
When the angular velocity-based Coriolis force is applied onto a tine in the direction of the Y axis while the tine vibrates in the direction of excitation, that is, along the X axis, the motion of the tine changes from unidirectional vibrations along the X axis to a rotational movement with distortion of the free end. Decomposition of the rotational movement into vectors of the X axis and the Y axis (perpendicular to the X axis) results in vibrations in the direction of excitation (excited vibrations) and vibrations in the direction of detection (detected vibrations). As for each tine, the frequency of the detected vibrations caused by the Coriolis force inevitably coincides with the frequency of the excited vibrations. As generally known, it is required to make the resonance frequency in the direction of the detected vibrations coincide with the resonance frequency in the direction of the excited vibrations in order to attain the maximum amplitude of the detected vibrations due to the Coriolis force. The greater amplitude of the detected vibrations and increase in the displacement of the tine are essential for the higher sensitivity of detection of the Coriolis force.
The conventional vibration-sensing element described above steadily excites vibrations (excited vibrations) of each tine along the X axis and detects the Coriolis force-based vibrations (detected vibrations) of the tine along the Y axis. This excitation and detection process is executed for the respective tines of the vibration-sensing element. In order to enhance the sensitivity of detection of the Coriolis force with the conventional vibration-sensing element, it is accordingly essential to make the resonance frequencies in the direction of the excited vibrations of the respective tines coincide with each other as well as to make those in the direction of the detected vibrations coincide with each other.
Each tine generally has a resonance frequency fxi along the X axis and a resonance frequency fyi along the Y axis, where i represents a corresponding tine number. The resonance frequencies fxi and fyi vary with the variation in the mass of the tine and the orientation of the mass variation. Adjustment of the resonance frequencies fxi and fyi by mass regulation should be repeated for all the tines included in the vibration-sensing element. This adjustment process requires much labor and time.